What counts as "very fast" is a matter of definition, but a common one is speeds at least 200 km/h (124 mph). However, high-speed trains usually run at 250 - 300 km/h (155 - 186 mph). The trains themselves are usually streamlined, with an airplane-like or missile-like appearance, thus "bullet trains". However, they use wheels on steel rails, like other trains. This makes them capable of using older rail lines, which they often do, though they go fastest on lines specially built for high-speed duty.